For the synthesis of polysilanes, the almost only one method available in the prior art was by condensing dichlorosilane in the presence of metallic sodium. This method, however, had several problems including difficulty of reaction control, low yields of high molecular weight polysilanes, and formation of insoluble polymers as by products.
To overcome these problems, the following polysilane preparing methods were proposed, but these methods yet had some problems and were unsuccessful in fully solving the above-mentioned problems.
(1) Polysilanes are produced by dewatering condensation of RSiH.sub.3 in the presence of Cp.sub.2 MR.sub.2 complexes wherein M is Ti or Zr. See J. H. Harrod, ACS, Polym. Prepr., 28, 403 (1987). There are obtained polysilanes having a degree of polymerization of about 20. This method is unsuitable for preparing polysilanes having a higher degree of polymerization.
(2) Polysilanes are produced by anionic polymerization using biphenyl crosslinking agents. See Sakurai et al., Proceedings of the 56th Japan Chemical Society, Spring Meeting, 1988, 1 IV 03. This method is not commercially acceptable since the biphenyl crosslinking agents are difficult to synthesize.
(3) The prior art method is improved by adding crown ethers. See Fujino et al., Proceedings of the 56th Japan Chemical Society, Spring Meeting, 1988, 1 IV B12. The addition of crown ethers can promote reaction, yet the final yield of polysilanes remains substantially unchanged compared to the prior art method.